In recent years, with the development of a chip technology of CCD or CMOS and the like, a pixel size of the chip becomes smaller and smaller, and a requirement for an imaging quality of a matching optical system also becomes higher and higher, while a size of an optical lens mounted on electronic products such as a mobile phone or a digital camera becomes smaller and smaller, so that the lens develops rapidly towards a miniature and high pixel trend. At present, a common high pixel thin type lens mainly makes use of a five lens, as described in U.S. Pat. No. 8,369,027. However, a requirement for a pixel and an imaging quality of a miniaturized camera lens is further promoted because of developments of portable electronic products. The known optical system can't satisfy higher photography demand. Currently, more lenses are used to further promote the imaging quality, but the size of the lens is hard to control, and therefore commercialization is limited. A lens with good imaging quality and with a length not much influenced by number of lenses is needed.